The present invention relates to injection molding gating and more particularly, to an improved gating needle for use in an injection molding sprue bushing.
A variety of gating systems have been commonly used in the past with varying degrees of success for the injection molding of different materials in various applications. Proper gating is important in injection molding because it provides the necessary amount of heat to the mold cavity gate area to maintain the injected melt in a molten condition as it passes through the mold gate on its way to the mold cavity. It is desirable to maintain as high a melt temperature as possible in the mold gate area as the melt flows from the bushing through the gate and into the mold cavity, yet it is likewise desirable to avoid excessive heat transfer to the cooled mold blocks surrounding the mold gate. Proper gating provides the most efficient manner of injection molding.
Previous attempts at controlling the temperature of the gate area have been accomplished by the use of a heated torpedo disposed within a mold block and adjacent the gate area. Where the heated torpedo is internally heated, and the internal heater does not extend within the torpedo to a position very close to the gate area, it is difficult to maintain the temperature of the melt at the torpedo tip at a proper constant desired temperature. Other gating systems have used a central conductive pin which is driven by a reciprocating drive mechanism in which the central pin seals the mold gate at the end of every molding cycle. Such drive mechanism add to the cost and complexity of the overall injection molding system. Additionally, the central pin must be specially fabricated to withstand the repeated force of its closing the mold gate.
The present invention is directed to an economical injection molding sprue bushing gating needle which overcomes the aforementioned disadvantages. The present invention is characterized by a needle assembly which is slidingly disposed within a recess at the sprue bushing outlet end. The needle assembly includes an elongated needle member having a first end, a second end and an intermediate portion therebetween which has at least three outwardly projecting ribs. The ribs are received by a recess or annular opening disposed at the outlet end of a sprue bushing. When the needle assembly is in place within the sprue bushing outlet recess, its first end extends for a preselected distance past the sprue bushing outlet end while its opposing second end extends upstream into the center of the sprue bushing melt runner passage. The gating needle has an internal heat transfer means in the form of either a highly thermally conductive material disposed in its central interior portion or it may include a hollow sealed tube or "heat pipe"]containing a vaporizable liquid held under a partial vacuum. In either instance, the internal heat transfer means serves to provide heat towards the first needle end during the injection of melt into a mold cavity.
Accordingly, it is a general object of the present invention to provide an improved gating system for an injection molding sprue bushing.
Another object of the present invention is to provide an improved gating needle for use with a sprue bushing which is displaceable between a first position and a second position wherein the gating needle includes an elongated needle portion slidingly held within the center of the sprue bushing internal melt runner passage and wherein the needle displaces a preselected distance to its second position generally adjacent the mold cavity gate by the pressure of the injected melt.
A further object of the present invention is to provide an improved gating needle for use within a sprue bushing having a generally circular cavity in its outlet end wherein an elongated needle is supported therein by a plurality of radial fins and wherein the gating needle is capable of restricted reciprocating movement within the melt runner passage of the sprue bushing.
Yet another object of the present invention is to provide a displaceable floating gating needle for use in an injection molding sprue bushing wherein the gating needle is capable of longitudinal movement within the sprue bushing melt runner passage, such that the gating needle maintains a preselected clearance with the mold cavity gate.
Still another object of the present invention is to provide an improved injection molding gating needle for use with a sprue bushing wherein the gating needle has an elongated body portion disposed within the general center of the sprue bushing melt runner passage which body portion extends longitudinally within the melt runner passage from a heated portion thereof to a mold gate and wherein the elongated body portion contains a heat pipe for transferring heat from the rear of the body portion to the front of the body portion.
These and other objects, features and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings wherein like reference numerals refer to like parts.